Sexual and individual foraging segregation in Gentoo penguins Pygoscelis papua from the Southern Ocean during an abnormal winter
Résumé
Knowledge about sexual segregation and gender-specific, or indeed individual specialization,
in marine organisms has improved considerably in the past decade. In this context, we
tested the ªIntersexual Competition Hypothesisº for penguins by investigating the feeding
ecology of Gentoo penguins during their austral winter non-breeding season. We considered
this during unusual environmental conditions (i.e. the year 2009 had observations of
high sea surface and air temperatures) in comparison with the long term average at Bird
Island, South Georgia. Through conventional (i.e. stomach contents) and stable isotopic
values from red blood cells, plasma and feathers of both male and female Gentoo penguins,
we showed that there were significant differences between sexes, with males feeding mainly
on fish (54% by mass) followed by crustaceans (38%) whereas females fed mainly on crustaceans
(89% by mass) followed by fish (4%). Themisto gaudichaudii was the most important
crustacean prey for males (64% by mass; 82% by number; 53% by frequency of occurrence)
and females (63% by mass; 77% by number; 89% by frequency of occurrence), contrasting
with all previous studies that found Antarctic krill Euphausia superba were generally the main
prey. Stable isotopic data showed that, in terms of habitat use (based on δ 13C), there were
significant differences in short-term carbon signatures between males and females (based
on plasma and red blood cells), suggesting that both sexes explored different habitats, with
females exploring more offshore pelagic waters and males feeding more in coastal benthic
waters. Based on δ 15N, males fed on significantly higher trophic level than females (based
on plasma and red blood cells), in agreement with our diet results., Thus, Gentoo penguins
behave in a similar manner to other non-breeding penguins species (e.g. king, macaroni
and rockhopper penguins), albeit at a smaller spatial scale (as they do not disperse as these
other penguins do), in that they have a wider habitat and trophic niche during the Antarctic
Winter (in comparison to Summer). We also detected individual specialization in feeding/trophic levels for each gender, with certain males feeding mainly on fish and certain females
mainly on crustaceans, which may be driven the prevailing environmental conditions that
lead individuals to search for alternative prey, and cause sexual diet segregation. Our results
provide further information to help improve understanding about sexual segregation and individual
specialization of marine organisms, while contributing valuable information on the winter
diet for Antarctic monitoring programs and for modelling Antarctic marine food webs.